1. Field of the Invention
The present invention relates to a device and a method for recording and reproducing data included in program content for digital broadcasts.
2. Description of the Related Art
Digital broadcasting, as provided in Japan, North America and Europe, is a configuration wherein video and audio data, encoded in accordance with MPEG2 (Moving Picture Experts Group Phase 2) standards, are multiplexed in accordance with MPEG2-TS (Moving Picture Experts Group Phase 2-Transport Stream) standards. MPEG2-TS recording and reproduction is described, for example, in Japanese Patent Application Laid-Open No. 2004-336332, No. 2005-167649 and No. 9-312634.
According to the description given in Japanese Patent Application Laid-Open No. 2004-336332, the objective is “to provide the digital broadcast receiver that, without causing an underflow or an overflow of the buffer of the digital broadcast receiver, enables normal AV reproduction or double-speed special AV reproduction from a storage device wherein stored are MPEG2-TS data to which a time stamp has been added”, and the means for achieving this objective is “the digital broadcast receiver comprising
buffer remaining volume monitoring means, for controlling starting and halting of reading by the data reading means in accordance with the volume of the data remaining in the buffer after a video or audio transport stream has been multiplexed,
wherein, at the time of normal AV reproduction, the switching means controls output time, and the output time control means adjusts the output time equal to the time for a broadcast wave for performing AV reproduction, and
wherein, at the time of special AV reproduction, such as double-speed reproduction, the switching means does not control output time, and the buffer remaining volume monitoring means monitors the buffer volume and controls the starting and halting of reading by the data reading means”.
Also, according to the description given in Japanese Patent Application Laid-Open No. 2004-336332, “when normal AV reproduction is to be performed by reading MPEG2-TS data stored in the storage device, synchronous reproduction using PCR is enabled, and since reproduction is performed by synchronizing 27 MHz clocks on a transmission side and a reception side, the underflow or the overflow of an AV buffer unit 206 does not occur”.
According to the description given in Japanese Patent Application Laid-Open No. 2005-167649, the problem with the invention is that “since MPEG2-TS is formed by multiplexing a transport packet that includes received video data, in MPEG2-TS, transport packets for an arbitrary channel are contiguously arranged at intervals, and at these empty intervals, transport packets for one or a plurality of different channels are present. Therefore, an appropriate control is required only when the arbitrary transport packets in the MPEG2-TS are to be extracted from the MPEG2-TS and recorded on a hard disk, or displayed on a screen, and how the control should be exercised is a problem”. Further, means for resolving this problem is “a storage/output device, according to this invention, comprising
acquisition means, for obtaining each of a plurality of contiguous data sets,
writing means, for adding, to each of the obtained data sets, a special time stamp that represents information related to the temporal position of the data, and then storing the special time stamp in the storage means,
reading means, for reading from the storage means each set of the plurality of stamped data, which are data to which the special time stamp has been added, and for outputting, as read-out data, the individual stamped data that have been read, or stamp-free data obtained by removing the special time stamp from the stamped data; and
acquisition and output means, for obtaining and outputting the read-out data that are output by the reading means,
wherein the reading means selectively performs the output of the read-out data at the time that does not depend on the special time stamp added to the individual stamped data that has been read and the output of the read-out data at the time that depends on the special time stamp added to the individual stamped data that has been read”.
In addition, as described in Japanese Patent Application Laid-Open No. 2005-167649, “the decoder 4 performs flow control, e.g., controls the reading unit 12 by transmitting a request signal to the reading unit 12, and permits the reading unit 12 to output, at an arbitrary timing (i.e., a timing consonant with the frequency of a clock signal oscillating without any control), a plurality of data sets that are obtained by reading from the storage medium 13. For example, when the buffer 85 is vacant (or the quantity of accumulated second selected packets is small), the decoder 4 performs flow control, and obtains a plurality of packets read at the arbitrary timing. It should be noted that during the flow control process the decoder 4 manages the buffer 85. For example, to perform flow control, the decoder 4 maintains the quantity (e.g., eighty percent of the buffer 85) of second selected packets stored in the buffer 85 so that it is larger than the quantity (e.g., twenty percent of the capacity of the buffer 85) when the real time display or the special time stamp control is performed. The data stored in the buffer 85 are erased by the decoder 4 or the controller 71 when the control process is switched between the flow control and the real time display or the special time stamp control.”
According to the description given in Japanese Patent Application Laid-Open No. 9-312634, the objective is “a system clock reproduction device having a configuration, provided at a low cost, that prevents unauthorized system clock reproduction that causes a PCR reception abnormality”. And the means for achieving this objective is “the fixed value generation device 2140 calculates and holds the convergent value of the control voltage for the VCXO 1140 at the normal PCR reception time, and when the PCR abnormality detection device 2100 detects a PCR reception abnormality, the control voltage of the VCXO 1140 is immediately changed to the output of the fixed value generation device 2140, and normal system clock reproduction is continued.”
However, the following problems are not disclosed in the technical ideas presented in Japanese Patent Application Laid-Open No. 2004-336332, No. 2005-167649 and No. 9-312634.
In Japanese Patent Application Laid-Open No. 2004-336332, it is assumed that during the normal reproduction process, the recording/reproducing device generates a system clock based on the same PCR as that used to receive and view digital broadcasting. The PCR is reference information for reproducing a clock that is synchronized (simply clock timing need be matched, even when a phase is shifted) with a system clock that was used to generate a program or content, and in Japanese, the PCR may be referred to as a reference value for the program time standard. In other words, the PCR is reference information for synchronizing a system clock used for encoding with a system clock used for decoding. The PCR can also be referred to as reference information used for correcting a system clock. Assume that normal reproduction is to be performed for MPEG2-TS, for which an abnormality is present in the PCR, e.g., the PCR is discontinuous or the PCR includes a large jitter (a shift in the time axial direction or a fluctuation in a delay time: When an electric signal is to be transmitted, for example, the delay time is extended or reduced due to the characteristic of the transmission path or the external environment, and the signal transmission period is shifted slightly. This shift in the time-axial direction is called a jitter). In this case, a system clock determined by the MPEG standards might not be stably generated. Example causes for the generation of a large jitter in the PCR can be: a defect in a device on a broadcast station side (a broadcasting accident); a defect in means for generating a time stamp to be added during recording; a defect in means that controls a reproduction timing based on a time stamp; and a delay and fluctuation of data broadcast via a network. Further, example causes of the PCR becoming discontinuous can be: omitting part of packets during editing of program content by deleting a part, or because of a reception failure that occurred during the recording of digital broadcasting. It should be noted that, according to the embodiment of the present invention, a time stamp represents the timing for outputting content data to a buffer that will be described later, and that is to be added to content data when the content data are recorded on a recording medium. This time stamp differs from a time stamp such as a DTS (Decoding Time Stamp) or a PTS (Presentation Time Stamp) that is included in advance in a transport packet.
Further, it is thought that various makers produce and sell various digital broadcasting recording devices. There is a case wherein, as a common standard for the makers, adding a time stamp is defined for recording content; however, this accuracy varies. Then, when the MPEG2-TS content that conforms to the common standards is reproduced from the recording device based on the time stamp, the accuracy of the PCR that is handled between the digital broadcasting recording devices might be different. In this state, assume that content is recorded on a recording medium by a device that does not add a time stamp, or by a device that adds a comparatively low accuracy time stamp to recording content, and another device is employed to reproduce this recording medium. In this case, since the time stamp is not normal for the reproduction device, i.e., the time stamp is not present or the accuracy of the time stamp is comparatively low, accordingly, the PCR reproduced based on the time stamp is abnormal, and a stable system clock can not be generated.
When a stable system clock can not be generated due to the above described factor, it is believed that an overflow or an underflow will occur at the buffer (STD buffer) located at the front stage of the decoder. Then, an image might be deteriorated, e.g., a block noise would occur in a picture output by the decoder, or the video output by the decoder would be frozen.
When, even if an overflow or an underflow does not occur in the buffer, a stable system clock can not be controlled within the range that is guaranteed relative to the allowable deviation of the color frequency for an image, the correct color might not be reproduced (displayed).
That is, when a stable system clock can not be generated, a problem arises in that video data and/or audio data included in program data and content data can not be correctly recorded, or reproduced.
Furthermore, as another problem, even when a stable fixed clock not related to a PCR and generated by a quartz oscillator is employed for the reproduction of content to which an abnormal time stamp is added, video data and/or audio data included in program data and content data can not be correctly reproduced.
According to Japanese Patent Application Laid-Open No. 2005-167649, when a packet recorded on a recording medium is to be read to a buffer for decoding, an arbitrary timing that is not related to a PCR is employed in consonance with the quantity of packets stored in the buffer. Therefore, the content data can be somewhat correctly reproduced, regardless of the presence or absence and the level of accuracy of the time stamp. However, the reproduced content may be shifted away from a system clock that was being employed when the content was prepared.
In Japanese Patent Application Laid-Open No. 9-312634, the prevention of unauthorized system clock reproduction that occurs at the time of a PCR reception abnormality is described. However, no consideration is given to a problem that occurs when content is recorded on a recording medium. In addition, no consideration is given to a problem that occurs when a different device is employed to reproduce content recorded on a recording medium, and an abnormal PCR or time stamp has been added to the content. As a result, normal reproduction of the content might not be possible.
These problems are encountered not only with MPEG2, but also with other standards, such as H.264.